I. Field of the Invention
The present invention relates generally to tool holders of the type used in industrial applications.
II. Description of the Prior Art
In industrial applications, such as CNC machines, cutting tools are typically mounted to a tool holder which, in turn, is mounted to the rotary driven spindle of a machine. For example, for a CNC machine, HSK tool holders with collet front ends are commonly used since such tool holders may be readily and automatically mounted to the CNC machine spindle. These previously known HSK tool holders, however, have suffered from a number of disadvantages.
One disadvantage of the previously known HSK collet type tool holders is that only a minimal adjustment of the axial position of the tool relative to the tool holder could be achieved. This minimal tool adjustment is typically in the range of about one-quarter of an inch.
A still further disadvantage of the previously known HSK tool holders is that the HSK tool holders utilized collapsible collets in order to secure the tool to the tool holder. These collapsible collets, however, are not known for maintaining precision alignment of the tool relative to the tool holder axis. Furthermore, such tool holders allow tool spin out, i.e. rotation of the tool relative to the collet. These tool holders do not provide a positive drive between the tool holder and the tool. Instead, the tool holder relied solely upon the collapsible collet to secure the tool to the tool holder. As such, tool spin out at relatively low torque forces occurred.
A still further disadvantage of the previously known HSK tool holders is that, in the event of tool spin out, the tool oftentimes scores and otherwise damages the internal bore on the tool holder. The previously known HSK tool holders, however, are non-repairable so that damage to the tool holder from tool spin out oftentimes requires that the entire tool holder be scrapped.
The present invention provides a tool holder which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the tool holder of the present invention comprises a tool body having a cylindrical bore with a predetermined inside diameter. The body is preferably of a standard configuration, e.g. an HSK tool holder body, such that the tool holder of the present invention is interchangeable with existing standard tool holders.
The tool holder further comprises an elongated cylindrical insert having a throughbore or collet pocket. The insert has an outer diameter slightly larger than the inside diameter of the body cylindrical bore so that the insert is insertable into the body cylindrical bore only when the body is heated to a predetermined elevated temperature. At that elevated temperature, e.g. 1000xc2x0 F., the body thermally expands to an extent such that the inside diameter of the body bore is greater than the outer diameter of the insert. With the body thermally expanded, the insert is inserted into the body bore so that, upon cooling of the body, the body and insert are rigidly and concentrically secured together.
A free end of the body includes external threads which threadably cooperate with an internally threaded collet. The shank of the tool is then inserted through the collet and into the insert throughbore so that, upon subsequent tightening of the collet onto the insert, the collet rigidly and coaxially secures the tool holder shank to the insert and thus to the tool holder body. The collet may be either of the previously known collapsible type, or a precision single slot collet.
In order to provide positive locking of the tool shank to the insert against relative rotation and thus minimize the chance of tool spin out, the inner end of the tool shank includes a noncircular portion, typically two diametrically opposed flats. These flats are received within a recess of a boss which is longitudinally slidably mounted within the insert throughbore. The outer periphery of the boss is noncircular, and preferably square, and longitudinally slides within a like shaped channel formed at the inner end of the insert throughbore. Thus, although the boss is longitudinally slidably mounted within the insert throughbore, rotation of the boss, and thus the tool holder shank, relative to the insert is precluded.
In order to adjust the position of the boss within the insert throughbore, and thus adjust the extent of extension of the cutting tool from the insert, the insert channel, i.e. the portion of the insert in which the boss is axially slidable, is internally threaded. The threaded fastener is then threadably mounted to the insert channel. The threaded fastener is secured to the boss so that the fastener and boss are secured against axial displacement relative to each other, but can rotate relative to each other. Consequently, rotation of the fastener within the insert channel axially adjusts the position of the boss within the channel and thus the longitudinal position of the tool relative to the insert. Axial adjustment of about a minimum of one inch of the boss, and thus of the tool, is achieved.
As will become hereinafter more clearly apparent, the tool holder of the present invention enjoys all of the advantages of the previously known tool holders which utilize collets to secure the tool shank to the tool holder. Additionally, however, the tool holder of the present invention enjoys adjustability of the extension of the cutting tool from the insert as well as modularity, i.e. the inserts and bodies of the tool holder may be maintained as stock items. Furthermore, in the event of damage to the insert by excessive torque, the insert may be freely removed from the body by simply reheating the body, removing the damaged insert, and inserting a new insert. Replacement of the insert, of course, is much less expensive than replacement of the entire tool holder body.
The use of inserts also allows length extension to be incorporated in the insert while maintaining the tool holder body in standard lengths.